In modern transmitters the power amplifier (PA) is one of the dominating current consumers and reducing current consumption is of ongoing concern to transmitter design. Attempts to reduce the current consumption of the PA, i.e., increase the efficiency of the PA, can be based on biasing the PA with as low a quiescent current as possible. However, increasing the efficiency of the PA comes at the cost of a loss of linearity of the PA. Generally speaking the linearity of the PA is inversely proportional to the efficiency of the PA, the higher linearity the lower power efficiency. Considering the higher bitrates and more complex modulation schemes associated with today's transmissions, the linearity requirements are increased and therefore the power consumption is increased.
To achieve good linearity combined with good efficiency, a technique known as digital pre-distortion can be applied. Once the behavior of the PA is known the input of the PA can be pre-distorted with the “inverse” of the expected error. The theory is that the desired signal plus the “inverse” of the distortion should generate only the wanted signal after the PA.
The digital pre-distortion technique assumes that the characteristics of the PA are well understood, i.e., both over process, voltage, and temperature (PVT), however, this knowledge is not trivial to achieve due to the large number of combinations of PVT variations and any deviation in the behavior of the PA, from the expected behavior of the PA will result in a degradation of the linearity associated with the PA when digital pre-distortion is applied.
Accordingly, it would be desirable to provide devices, systems and methods for reducing the current consumption while maintaining linearity of power amplifiers in transmitter systems.